Nanometer-scale science has been an exciting area of recent research investigations with fundamental as well as technological significance. As a result, new physical phenomena resulting from novel nanoelectronic devices have been discovered and continue to be anticipated. Based on their versatile electronic properties and adaptability to a broad range of processing methods, conjugated systems have been applied successfully to the area of organic electronics (1-10). However, the development of fundamental methods for the design and development of polymer-based nanoelectronics is still in its infancy.
In recent years, characteristics of organic electronic materials have been remarkably improved. In particular, the so-called organic bistable materials where, if a voltage is applied to the material, an electric current in a circuit rapidly increases at a voltage above a threshold value (i.e., the circuit is ON) as compared to a much lower current when the voltage is below the threshold value (i.e., the circuit is OFF). This switching phenomenon has found applications for switching elements for, e.g., driving the organic EL display panels or for high-density memories.
Most bulk conducting polymer systems that have been created consist of regions of inhomogeneity. The investigation of processes in pure crystalline materials is critical in ascertaining the inherent electronic properties of polymer nanoelements. The searches for nanosized and molecular switches have been of critical importance for the development of nanoelectronics. Potential switches include interlocked co-comformers (6), conjugated organic oligomers (8) and redox-induced junction formation (9). Similar to oligomers, conjugated polymers also showed switching behaviors. The first reported conducting polymer switch was based on polyaniline (7). Polyaniline nanojuctions were electrochemically synthesized as the bridge between gold electrodes. A decrease in switching time was observed when the electrode gap decreased to one nanometer. This decrease in switching time was thought to be one of the characteristics of the single crystalline domains, although the crystalline nature of the junction was not experimentally verified. Although highly ordered structures have been prepared by electrochemical epitaxial polymerization (10), solution spin-coating on functionalized surface (11) and solid-state polymerization of pre-organized monomers (12), nanostructures based on single crystals of conducting polymer have not been reported. To date, polythiophenes together with polyanilines and polypyrroles represent the most important group of conductive polymers for application in nanoscale molecular switching devices.